Passive and reverse passive agglutination tests are well known serological procedures.
The usual carriers are erythrocytes of animals, i.e. birds or mammals, or cells of microorganisms. These carriers may have absorbed antigen or antibodies and are known as sensitized cells. Sensitized cells will undergo agglutination reactions with complementary reagents, containing either antibodies or antigens. The agglutination test is a method for optically testing the presence of antigens or antibodies. The agglutinated reaction product will eventually flocculate and precipitate to the bottom of the test vessel.
Agglutination tests are widely employed. They are, however, subject to some difficulty because of an undesirably high number of false positive reactions due to the presence of cross-reacting substances. There are a number of factors which cause these non-specific reactions which give rise to false positives. Typically, they may be antibodies which react with the carrier erythrocytes or cells. Collectively, these factors are, hereinafter, referred to as "anti-carrier". In order to limit the number of false positives, attempts are made to remove anti-carriers by absorption as a routine procedure prior to application of the passive agglutination test.
The absorption removal of anti-carrier is a well known technique. Normally, the absorbents are the same erythrocytes or cells used as carriers. Typically, they are erythrocytes from birds or mammals, although erythrocytes from reptiles or crustaceans may also be employed. All such erythrocytes are referred to herein as animal erythrocytes. The most widely employed are from chickens, turkeys, sheep, cattle, pigs, rabbit or humans. Erythrocytes from chickens and cattle are generally preferred because of their ready availability.
The preferred cellular microorganisms are those such as Saccharomyces cerevisiae and Serratia marcescens.
The absorbents are aldehyde fixed by, for example, immersion in 0.1% to 30% aqueous formaldehyde solutions at a temperature of from 4.degree. C. to 40.degree. C. for from one to 200 hours. Equivalent aldehyde fixation procedures employing, for example, acetaldehyde, gluteraldehyde or pyruvaldehyde are also known and can be employed in the practice of this invention.
Experience has established two principal difficulties with conventional absorbents. These are, (1) they do not remove all of the interfering reactants, and (2) the products produced by the reaction are difficult to remove, even with a high speed centrifuge. Accordingly, conventional absorbent procedures have not proved entirely satisfactory.
It is, therefore a principal object of this invention to provide novel absorbents which can be used to remove substantially all of the anti-carriers and other factors which interfere with the specificity and reliability of the passive agglutination test.